RFR: 8312132: Add tracking of multiple address spaces in NMT [v74]

[Johan Sjölen]

On Fri, 10 May 2024 12:11:56 GMT, Thomas Stuefe <stuefe at openjdk.org> wrote:

>> src/hotspot/share/nmt/vmatree.hpp line 151:
>> 
>>> 149: 
>>> 150:   SummaryDiff release_mapping(position from, position sz) {
>>> 151:     Metadata empty;
>> 
>> Just a nit, but instead of the Metadata::Metadata() ctor creating an empty object, could we possibly scrap the default ctor and have an explicit static constexpr Metadata empty with invalid stackindex and mtNone as ctor args? I find that nicer to read.
>
> Oh, another thing, maybe rename this to something else. `Metadata` has a clear meaning in hotspot. Maybe something like RegionData?

Hi Thomas, what naming scheme should I use for the empty static RegionData? `EmptyRegionData` or `empty_regiondata`? It can't be `constexpr`, but we can make it `const`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/18289#discussion_r1598288301